This invention relates to device for detection of radon gas employing a detector material which records the impact of alpha particles emitted by radon and derived radioactive decay products. More particularly, this invention is an improvement of the compact radon detector described in U.S. Pat. No. 4,518,860 which is incorporated by reference herein for extensive discussion of radon detection. In general, the objective of this invention is to provide not only an effective device for detection of radon, but in addition to provide a radon detector which is dimensioned for convenient personal use as well as in permanent installations.